MessagePort

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2015.

* Some parts of this feature may have varying levels of support.

Note: This feature is available in Web Workers.

The MessagePort interface of the Channel Messaging API represents one of the two ports of a MessageChannel, allowing messages to be sent from one port and listening out for them arriving at the other.

MessagePort is a transferable object.

EventTarget MessagePort

Instance methods

Inherits methods from its parent, EventTarget.

postMessage()

Sends a message from the port, and optionally, transfers ownership of objects to other browsing contexts.

start()

Starts the sending of messages queued on the port (only needed when using EventTarget.addEventListener; it is implied when using onmessage).

close()

Disconnects the port, so it is no longer active.

Events

Inherits events from its parent, EventTarget.

message

Fired when a MessagePort object receives a message.

messageerror

Fired when a MessagePort object receives a message that can't be deserialized.

Example

In the following example, you can see a new channel being created using the MessageChannel() constructor.

When the IFrame has loaded, we register an onmessage handler for MessageChannel.port1 and transfer MessageChannel.port2 to the IFrame using the window.postMessage method along with a message.

When a message is received back from the IFrame, the onMessage function outputs the message to a paragraph.

js
const channel = new MessageChannel();
const output = document.querySelector(".output");
const iframe = document.querySelector("iframe");

// Wait for the iframe to load
iframe.addEventListener("load", onLoad);

function onLoad() {
  // Listen for messages on port1
  channel.port1.onmessage = onMessage;

  // Transfer port2 to the iframe
  iframe.contentWindow.postMessage("Hello from the main page!", "*", [
    channel.port2,
  ]);
}

// Handle messages received on port1
function onMessage(e) {
  output.innerHTML = e.data;
}

For a full working example, see our channel messaging basic demo on GitHub (run it live too).

Specifications

Specification
HTML
# message-ports

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobileserver
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
MessagePort
close
message event
messageerror event
postMessage
options.includeUserActivation parameter
Non-standard
start
Available in workers

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
Partial support
Partial support
No support
No support
Non-standard. Check cross-browser support before using.
See implementation notes.
Has more compatibility info.

See also